This research project is designed to analyze interactions between postsynaptic target neurons and presynaptic axons which result in specific and non-specific synapse formation in regenerating and developing central nervous tissue. In particular, the plastic response of embryonic neurons will be compared with the regenerative responses of adult neurons. Specifically, implants of embryonic CNS tissue will be allowed to interact with the septal and/or hippocampal regions of the adult rat brain by placing them in cavities produced by removing the entorhinal cortex and/or transecting the fornix-fimbria. Utilizing this intracephalic implantation technique two environments can be established in which to study axonal growth and synaptogenesis; one which allows regenerating axons from the adult CNS to interact with embryonic neurons, and another which permits axons from embryonic neurons to form synapses in an adult postsynaptic environment. The interactions which occur will be assessed using neuroanatomical tracing techniques such as autoradiography, horseradish peroxidase, acetylcholinesterase staining, and histochemical fluorescence techniques.